This invention relates to a motor pump. More particularly, it relates to a variable reluctance motor which has a rotor assembly that forms the impellor of a centrifugal pump.
Variable reluctance motors are well known in the prior art and various exemplary designs of such motors may be seen in U.S. Pat. No. 3,700,943 to Heintz, 3,700,944 to Heintz et al and 3,714,533 to L. E. Unnewehr, one of the present inventors. These brushless motors employ an exciting winding and a magnetic circuit to produce mechanical torque which is substantially proportional to the square of the winding ampere-turns and to the time rate of change of the magnetic circuit permeance (reciprocal of reluctance), which is a function of the displacement of the rotor in the motor. Typically, these motors employ a stator containing a motor winding and a rotor containing ferromagnetic elements spaced from one another. Displacement of the rotor relative to the stator produces a variation in reluctance, and, hence, permeance of the magnetic circuit of the motor winding. Of course, displacement of the rotor relative to the stator also produces a variation in the self-inductance of the motor winding, this self-inductance being directly related to the permeance of the magnetic circuit.
The torque or force produced by a variable reluctance motor is proportional to the product of the square of the winding ampere-turns and the rate of change of permeance as a function of rotor displacement. From the preceding, it is apparent that motor torque or force that is positive with respect to some arbitrary reference can only be developed when winding ampere-turns are sustained during an interval in which the permeance increases with rotor displacement. Conversely, negative motor torque or force is developed when winding ampere-turns are sustained during an interval in which the permeance decreases with rotor displacement. In order to secure continuous rotation of the variable reluctance motor, it is necessary to apply ampere-turns to the motor winding during intervals of increasing permeance and to decrease or eliminate such ampere-turns during intervals of decreasing permeance.
From the above discussion, it is apparent that the winding of a variable reluctance motor must be excited from a time varying source, although current flow may be unidirectional. Furthermore, the time variations of the source must be synchronized with the mechanical rotation of the machine rotor so that winding current is supplied to the motor during intervals in which the permeance increases with displacement and so that such current is decreased or, preferably, interrupted during the intervals in which the permeance is decreasing with rotor displacement. When a time-invariant source of electrical energy, such as a direct current source, is used, a controller is required to produce synchronized pulsations of control circuits, such as that described in U.S. Pat. No. 3,714,533 mentioned above, also may be used with the motor pump.